Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted air charge and improving peak power outputs. In the turbocharged engines, airflow to the engine (hence the torque) may be regulated through the action of a throttle located at the engine intake. The boost pressure may be regulated through the actions of an exhaust bypass or wastegate (WG) coupled across an exhaust turbine and an air bypass or compressor recirculation valve (CRV) coupled across an intake compressor. The exhaust bypass may regulate the boost pressure by controlling the exhaust gas flow over the turbine (hence the power delivered to the compressor) and the air bypass may be commonly used for compressor surge management.
Typically during a tip-in where increased torque is demanded, the exhaust bypass is fully closed and the air bypass is also fully closed to provide increased power to the turbocharger as shown by Jankovic et. al. in US 20140260241, for example. By immediately closing both the exhaust bypass and the air bypass when torque demand is high, the air that is delivered to the engine is increased thereby increasing power that is delivered to the turbocharger. As a result, the boost pressure builds up.
The inventors however have recognized an approach to further increase the boost response and reduce turbo lag. In one example, the boost pressure may be increased by a method comprising: in response to an operator demand for additional torque from an engine (e.g., during tip-in), opening an air bypass around an air compressor which supplies air to said engine; and keeping said air bypass opened for a predetermined time and then closing said air bypass.
As one example, the air bypass may be opened in response to the said additional torque demand being greater than a threshold value. During the predetermined time when the air bypass is open, the boost pressure may not build up but the compressor may spin faster. Additionally, the turbo speed may rise at a faster rate when the air bypass is initially open. At the end of the predetermined time, when the air bypass is closed, this increased compressor speed then translates into achieving desired boost levels in less time than heretofore possible. In this way, turbo lag is decreased. Once the boost pressure reaches the target threshold, the throttle, the exhaust bypass, and the air bypass may be actively controlled to maintain the boost at the desired threshold. Overall, boosted engine performance is improved and turbocharger lag may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.